Acute myeloid leukemia with neutrophilic differentiation in a 12-year-old African lion (Panthera leo)

Daniela Losada-Medina Facultad de Medicina Veterinaria y de Zootecnia, Universidad Nacional de Colombia, Bogotá, Colombia

Search for other papers by Daniela Losada-Medina in
Current site
Google Scholar
PubMed
Close
 MV, MSc
,
Ana M. Henao-Duque Zoopath Laboratorio de Patología Veterinaria, Cali, Colombia

Search for other papers by Ana M. Henao-Duque in
Current site
Google Scholar
PubMed
Close
 MV, MSc
,
Diana I. Buitrago-Grisales Unit of Animal Welfare, Fundación Zoológica de Cali, Cali, Colombia

Search for other papers by Diana I. Buitrago-Grisales in
Current site
Google Scholar
PubMed
Close
 MV
, and
Juliana Peña-Stadlin Unit of Animal Welfare, Fundación Zoológica de Cali, Cali, Colombia

Search for other papers by Juliana Peña-Stadlin in
Current site
Google Scholar
PubMed
Close
 MVZ

Abstract

OBJECTIVE

To describe the clinical presentation, progression, and diagnosis of acute myeloid leukemia (AML) with neutrophilic differentiation in an African lion (Panthera leo).

ANIMAL

A 12-year-old male African lion kept at a zoological institution in Colombia.

CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES

The lion presented for anorexia, pale mucous membranes, and a hind limb lameness of acute onset. Feline leukemia virus testing was negative, and repeated blood samples revealed severe anemia, intermittent thrombocytopenia, lymphopenia, and neutrophilia. Coinfection with Anaplasma and Mycoplasma spp and chronic kidney disease were diagnosed based on clinicopathological findings.

TREATMENT AND OUTCOME

The lion received symptomatic treatment, doxycycline, and methylprednisolone or prednisolone. Euthanasia was elected due to clinical deterioration and unresponsive anemia, despite the resolution of Anaplasma and Mycoplasma spp infections. AML with neutrophilic differentiation was diagnosed based on bone marrow cytology, histopathology, and immunohistochemistry.

CLINICAL RELEVANCE

AML is a rare, aggressive hematopoietic disorder in domestic cats, although it has not yet been reported in nondomestic cats. This is the first description of the clinicopathological, histological, and immunohistochemical features of AML with neutrophilic differentiation in an FeLV-negative African lion that lacked circulating blasts.

Abstract

OBJECTIVE

To describe the clinical presentation, progression, and diagnosis of acute myeloid leukemia (AML) with neutrophilic differentiation in an African lion (Panthera leo).

ANIMAL

A 12-year-old male African lion kept at a zoological institution in Colombia.

CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES

The lion presented for anorexia, pale mucous membranes, and a hind limb lameness of acute onset. Feline leukemia virus testing was negative, and repeated blood samples revealed severe anemia, intermittent thrombocytopenia, lymphopenia, and neutrophilia. Coinfection with Anaplasma and Mycoplasma spp and chronic kidney disease were diagnosed based on clinicopathological findings.

TREATMENT AND OUTCOME

The lion received symptomatic treatment, doxycycline, and methylprednisolone or prednisolone. Euthanasia was elected due to clinical deterioration and unresponsive anemia, despite the resolution of Anaplasma and Mycoplasma spp infections. AML with neutrophilic differentiation was diagnosed based on bone marrow cytology, histopathology, and immunohistochemistry.

CLINICAL RELEVANCE

AML is a rare, aggressive hematopoietic disorder in domestic cats, although it has not yet been reported in nondomestic cats. This is the first description of the clinicopathological, histological, and immunohistochemical features of AML with neutrophilic differentiation in an FeLV-negative African lion that lacked circulating blasts.

History

A 12-year-old 190-kg intact male African lion (Panthera leo) housed at the Cali Zoo in Cali, Colombia, presented for anorexia, pale mucous membranes, steatorrhea and a mild right hind limb lameness. A CBC and serum biochemical profile (SBP) 2 months prior revealed a mild normocytic normochromic anemia (Hct, 23.8%; reference range [rr], 26.8 to 44.1) and total hypercalcemia (12.7 mg/dL; rr, 5.29 to 9.75 mg/dL). The lion had been vaccinated against rabies, feline panleukopenia, calicivirus, and herpesvirus within the 2 years before presentation.

Diagnostic Findings and Interpretation

Initial physical examination revealed dental calculus, low body condition score (2.5/5), and diffuse alopecia. A CBC and SBP showed a severe macrocytic normochromic anemia (Hct, 7.2%) and mildly elevated direct (0.19 mg/dL; rr, 0 to 0.08 mg/dl) and total bilirubin (0.94 mg/dL; rr, 0 to 0.85 mg/dl). The symmetric dimethylarginine concentration was above the upper reference limit for this biomarker in cats (16 µg/dL; upper limit of rr for cats, 14 µg/dL). Ultrasonographic examination of the thorax and abdomen revealed pericardial effusion, heterogeneous liver echogenicity, splenomegaly, enlarged left adrenal gland (cranial pole width, 7.0 mm; caudal pole width, 9.6 mm), and dilated left ureter (width, 6.3 mm). A neoplastic process was suspected, so a fine-needle aspirate of the spleen was performed, revealing a mixed lymphoid population predominated by small and medium lymphocytes, a few large lymphocytes and plasma cells, and several activated macrophages exhibiting erythrophagocytosis. Numerous megakaryocytes and metarubricyte aggregates were found. These findings suggested extramedullary hematopoiesis in the spleen, suspected to be secondary to immune-mediated hemolytic anemia.

Initial treatment consisted of ceftazidime (20 mg/kg, IV), methylprednisolone (2 mg/kg, IM, q 12 h for 2 days), and furosemide (1 mg/kg, IM, q 12 h for 4 days) as well as symptomatic care including nutritional supplements, gastroprotectants, and pain medication. The lion tested negative for FeLV, FIV, feline herpesvirus-1, feline panleukopenia virus, and Babesia, Bartonella, Ehrlichia, Hepatozoon, and Mycoplasma spp via PCR. Blood samples tested positive for Anaplasma sp via PCR, and structures morphologically consistent with Mycoplasma sp were observed on peripheral blood smears on day 7. A CBC and SBP revealed severe macrocytic hypochromic anemia (Hct, 16.8%), mild reticulocytosis (69.9 X 103 cells/µL; rr, 3 X 103 to 50 X 103 cells/µL), moderate thrombocytopenia (92 X 103 cells/µL; rr, 226 X 103 to 368 X 103 cells/µL), mildly elevated creatinine (3.8 mg/dL; rr, 0.89 to 3.23 mg/dL), moderately increased ALT (370.5 U/L; rr, 6.6 to 91.4 U/L), and severe hyperphosphatemia (21.36 mg/dL; rr, 4.42 to 5.8 mg/dL). A dipstick urinalysis of a sample collected from substrate revealed 3+ for blood, proteinuria (1+), and low specific gravity (1,018). Based on the new clinicopathological findings, anaplasmosis, mycoplasmosis, and chronic kidney disease (CKD) were diagnosed.

Treatment and Outcome

Treatment was adjusted, and the lion was administered doxycycline (5 to 7.5 mg/kg, PO, q 12 to 24 h for 19 days) and prednisolone (0.6 to 2 mg/kg, PO, q 12 to 24 h for 26 days). On day 17, the macrocytic hypochromic anemia (Hct, 13.2%) and hypercreatinemia (3.9 mg/dL) persisted, and moderate neutrophilia (24.9 X 103 cells/µL; rr, 3.9 X 103 to 18.54 X 103 cells/µL) developed. On day 19, the lion presented a seizure and received 1 L of whole blood from a clinically healthy 5-year-old intact female lion, with an Hct of 48%; and that was negative for Anaplasma, Babesia, Bartonella, Borrelia, Ehrlichia, Hepatozoon, and Mycoplasma spp, FeLV, FIV, and for antibodies to heartworm. Severe normocytic hypochromic anemia (Hct, 13.53%), mild thrombocytopenia (182 X 103 cells/µL), severe lymphopenia (0.3 X 103 cells/µL; rr, 0.76 X 103 to 7.22 X 103 cells/µL), mild hyperphosphatemia (6.87 mg/dL), moderate hypercreatinemia (4.07 mg/dL), moderate direct hyperbilirubinemia (0.21 mg/dL), and severe hypokalemia (2.65 mmol/L; rr, 3.56 to 4.17 mmol/L) were identified on CBC and SBP. Polymerase chain reaction testing of blood samples for Anaplasma sp was negative. On day 44, the lion had developed ischemic necrosis of the distal tail and a body condition score of 1/5, weight loss (body weight, 140 kg), pale mucous membranes, oral ulceration, multiple dermal erosions and excoriations, multifocal alopecia, scrotal dermatitis, right hind limb dermatitis and edema, and foot pad ulceration were found on physical examination. A CBC and SBP revealed a persistent severe normocytic normochromic anemia (Hct, 17.1%), moderate neutrophilia (20.1 X 103 cells/µL) with a mild left shift, moderately elevated direct bilirubin (0.19 mg/dL), moderate hyperphosphatemia (7.12 mg/dL), and severe hypokalemia (2.9 mmol/L) and hypercreatinemia (5.35 mg/dL). Serum symmetric dimethylarginine concentration had increased to 48 µg/dL. Abdominal ultrasonography showed heterogeneous echogenicity of the liver, dilated intrahepatic biliary ducts, and loss of kidney corticomedullary distinction. Euthanasia was performed due to the lion’s clinical deterioration and unresponsive anemia. Because a hematopoietic disorder was suspected, bone marrow aspirates and a postmortem examination were performed immediately after euthanasia. Gross postmortem findings included gastric mucosal erosion, irregular, asymmetric kidneys with poor corticomedullary distinction, and areas of renal cortical narrowing and cortical hemorrhage.

Histologically, bone marrow appeared hypercellular (> 90%) with numerous immature precursors in a paratrabecular distribution and extending toward the center of the marrow (Figure 1). Megakaryocytes, metarubricyte aggregates, and neutrophil and eosinophil granulocytes were occasionally seen. Bone marrow cytology revealed a predominant myeloid population with increased myeloblasts and progranulocytes (Figure 2), increased myeloid-to-erythroid ratio, and reduced erythroid and myeloid maturation (Table 1). Numerous metarubricytes with contracted nuclei and irregular and angular cytoplasm were observed. Paraffin-embedded bone marrow sections were stained with myeloperoxidase, CD11c, CD3, CD79a, and CD14. Most cells (70% to 80%) were positive for myeloperoxidase (Figure 1), while <30% were either CD3 or CD79a positive. The spleen exhibited severe multifocal erythrophagocytosis and proliferation of poorly differentiated blasts with occasional mitosis in the red pulp and marginal zone (Figure 3). Based on these findings, acute myeloid leukemia (AML) with neutrophilic differentiation in bone marrow and spleen was diagnosed.

Figure 1
Figure 1

Photomicrographs of sections of bone marrow from the African lion. A—High cellularity is evident (> 90%), with scattered megakaryocytes and no visible fat cells. H&E stain; bar = 100 µm. B—Most cells stain brown, indicating that these are positive for myeloperoxidase. Immunohistochemical stain specific for myeloperoxidase; bar = 100 µm.

Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.09.0530

Figure 2
Figure 2

Cytology of the lion’s bone marrow aspirates performed immediately after euthanasia. A—Myeloid lineage is predominant, and neutrophilic differentiation is observed as immature myeloid precursors, metamyelocytes, bands, and segmented neutrophils. Wright-Giemsa stain. B—A myeloblast (1), myelocytes (2), metamyelocytes (3), and a rubriblast (4) are shown. Wright-Giemsa stain.

Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.09.0530

Table 1

Bone marrow differential cell counts from a male African lion that was euthanized following clinical deterioration associated with acute myeloid leukemia with neutrophilic differentiation. Proportions of cell types were calculated in relation to 326 cells that presented adequate morphology for cell type classification.

Cell type Obtained value Reference range in cats
Myelopoiesis
 Myeloblasts (%) 11.6 0–0.4
 Promyelocytes (progranulocytes) (%) 27.3 0–3.0
 Myelocyte neutrophils (%) 16.2 0.6–8.0
 Metamyelocyte neutrophils (%) 11 4.4–13.2
 Band neutrophils (%) 8.2 12.8–16.6
 Segmented neutrophils (%) 3.9 6.8–22.0
 Eosinophilic myelocyte (%) 2.1
 Eosinophilic metamyelocyte (%) 0.6
 Eosinophilic band (%) 0.9
 Eosinophils (%) 0.3 0.8–3.2
 Basophils (%) 0 0–0.4
Erythropoiesis
 Rubriblasts (%) 0.6 0–0.8
 Prorubricytes (%) 1.5 0–1.6
 Rubricytes (%) 1.2 10.2–29.4
 Metarubricytes (%) 6.4 1.0–10.4
Lymphopoiesis
 Lymphocytes (%) 1.5 11.6–21.6
 Plasma cells (%) 0 0.2–1.8
Megakaryopoiesis
 Megakaryocytes (%) 0.3
Monopoiesis
 Monocytes (%) 4 0.2–1.6
 Histiocytes (%) 0
Unclassified cells (%) 2.4
Myeloid-to-erythroid ratio 8.4 1.2–2.2
Erythroid maturation index 1.9
Myeloid maturation index 0.43
Figure 3
Figure 3

Photomicrographs of sections of bone marrow and spleen from the African lion. A—Bone marrow cell population predominantly formed by blasts and undifferentiated round cells with occasional mitotic figures. H&E stain; bar = 20 µm. B—Detail of splenic marginal zone with similar undifferentiated round cells and blasts with scattered mitotic figures. Erythrophagocytosis, numerous siderophages, and a few neutrophils are also observed. H&E stain; bar = 20 µm.

Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.09.0530

Acute tubular necrosis, severe medullary nephrocalcinosis, and mild cortical fibrosis were found in both kidneys, along with acute interstitial nephritis of the left kidney. Focal biliary duct ectasia, diffuse cholestasis, mild multifocal hepatic centrilobular necrosis, a lung adenocarcinoma in situ, and thyroid follicular adenoma were also identified.

Comments

AML is a rare and aggressive myeloid neoplasm where clonal myeloid progenitor cells unable to mature accumulate in bone marrow and blood due to aberrant proliferation.1

AML is characterized by moderate to marked, persistent cytopenia in blood and ≥ 20% blasts in blood or bone marrow. Although the myeloblast percentage was 11.6% in the case of this lion, promyelocytes (27.3%) were counted as blasts for the total blast percentage calculation, as it has been previously performed in humans for the diagnosis of AML.2

AML generally results from acquired genetic abnormalities in stem cells, and cell type–specific mutations lead to a predominant cell lineage, allowing the classification of AML into subtypes. Neutrophilic (M2) differentiation has been most commonly reported in cats.3

Hallmarks of the M2 subtype proposed by the Animal Leukemia Study Group in 1991 were present in this case, including > 30% to < 90% blasts (including promyelocytes) calculated in relation to nonerythroid cells, > 10% of differentiated granulocytes, and < 20% of monocytic cells. These findings along with the elevated myeloid-to-erythroid ratio and the immunohistochemical findings supported the diagnosis of AML with neutrophilic differentiation in this lion.3 Even though hematopoietic tumors occur in captive wild felids, AML specifically has not been previously reported in nondomestic cats.

The diagnosis of AML is based on CBC findings, bone marrow cytology, and occasionally histopathology and immunohistochemistry. The bone marrow in AML is usually normo- to hypercellular, and there is a profound reduction in 1 or 2 cell lines with expansion of the neoplastic cells. Leukemic infiltration of the spleen may also occur, as described here.1

Cytochemical, immunophenotypic, and genetic features of neoplastic cells are used to classify AML in humans; however, cytochemical heterogeneity is observed in M2 cases in cats, and AML-associated antigens and genetic abnormalities require further investigation in this species.3 In our case, the markers CD3 and CD79a were used to rule out T-cell and B-cell leukemia/lymphoma, respectively, and CD11c and CD14 were assessed to rule out AML with monocytic differentiation. Myeloperoxidase staining confirmed neutrophilic differentiation in this lion.

AML carries a grave prognosis and rarely responds to chemotherapy protocols, and when present the response is commonly short-lived.1 The lion presented in this report had a short survival time and underwent rapid clinical deterioration in agreement with previous reports of AML in domestic carnivores.

This lion concurrently presented with other conditions, such as CKD, anaplasmosis, and mycoplasmosis. Anemia, dehydration, and hyperphosphatemia can also be secondary to CKD and can contribute to the development and progression of CKD as well. Persistent anemia and thrombocytopenia, signs of myeloid neoplasia that are often present in AML, were initially attributed to mycoplasmosis and anaplasmosis, respectively.3 Anemia, anorexia, and lameness are clinical signs of Anaplasma phagocytophilum infection in cats. However, a previous study4 failed to find a correlation between a positive PCR test result for A phagocytophilum and the presence of anemia or thrombocytopenia in apparently healthy adult feral cats. Asymptomatic A phagocytophilum infection is described in young lions as well. Thrombocytopenia is reported in cats with Mycoplasma haemofelis, and it appeared to resolve in this lion after doxycycline treatment.5

Nonspecific signs such as weakness, inappetence, and weight loss are associated with cytopenias and metabolic or paraneoplastic complications.1 Although circulating abnormal leukocytes are frequently seen in cats, they can be absent in some AML subtypes as reported here.3 Finally, acute leukemia is commonly associated with FeLV infection in cats; however, negative PCR testing did not indicate FeLV infection in this case.1

AML is a rare, aggressive neoplasm of domestic cats that has not previously been reported in nondomestic cats. Although this is the first report of AML in a nondomestic cat, AML should be considered as a differential diagnosis in FeLV-negative wild felids that have persistent cytopenias and lack circulating myeloblasts. Additionally, published criteria for classification of this disorder in dogs and cats may be useful for evaluation in nondomestic cats, but further study is warranted.

Acknowledgments

Dr. Diego Gomez and Dr. Brodie Reinhart provided valuable comments on previous versions of this manuscript.

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.

References

  • 1.

    Dobson J, Villiers E, Morris J. Diagnosis and management of leukaemia in dogs and cats. In Pract. 2006;28(1):28. doi:10.1136/inpract.28.1.22

    • Search Google Scholar
    • Export Citation
  • 2.

    Vardiman JW, Thiele J, Arber DA, et al. The 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and important changes. Blood. 2009;114(5):937-951. doi:10.1182/blood-2009-03-209262

    • Search Google Scholar
    • Export Citation
  • 3.

    Jain NC. Classification of myeloproliferative disorders in cats using criteria proposed by the animal leukaemia study group: a retrospective study of 181 cases (1969-1992). Comp Haematol Int. 1993;3(3):125-134. doi:10.1007/BF00186096

    • Search Google Scholar
    • Export Citation
  • 4.

    Galemore ER, Labato MA, O’Neil E. Prevalence of Anaplasma phagocytophilum infection in feral cats in Massachusetts. JFMS Open Rep. 2018;4(1):2055116917753804. doi:10.1177/2055116917753804

    • Search Google Scholar
    • Export Citation
  • 5.

    Lobetti R, Lappin MR. Prevalence of Toxoplasma gondii, Bartonella species and haemoplasma infection in cats in South Africa. J Feline Med Surg. 2012;14(12):857-862. doi:10.1177/1098612X12452495

    • Search Google Scholar
    • Export Citation
  • Figure 1

    Photomicrographs of sections of bone marrow from the African lion. A—High cellularity is evident (> 90%), with scattered megakaryocytes and no visible fat cells. H&E stain; bar = 100 µm. B—Most cells stain brown, indicating that these are positive for myeloperoxidase. Immunohistochemical stain specific for myeloperoxidase; bar = 100 µm.

  • Figure 2

    Cytology of the lion’s bone marrow aspirates performed immediately after euthanasia. A—Myeloid lineage is predominant, and neutrophilic differentiation is observed as immature myeloid precursors, metamyelocytes, bands, and segmented neutrophils. Wright-Giemsa stain. B—A myeloblast (1), myelocytes (2), metamyelocytes (3), and a rubriblast (4) are shown. Wright-Giemsa stain.

  • Figure 3

    Photomicrographs of sections of bone marrow and spleen from the African lion. A—Bone marrow cell population predominantly formed by blasts and undifferentiated round cells with occasional mitotic figures. H&E stain; bar = 20 µm. B—Detail of splenic marginal zone with similar undifferentiated round cells and blasts with scattered mitotic figures. Erythrophagocytosis, numerous siderophages, and a few neutrophils are also observed. H&E stain; bar = 20 µm.

  • 1.

    Dobson J, Villiers E, Morris J. Diagnosis and management of leukaemia in dogs and cats. In Pract. 2006;28(1):28. doi:10.1136/inpract.28.1.22

    • Search Google Scholar
    • Export Citation
  • 2.

    Vardiman JW, Thiele J, Arber DA, et al. The 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and important changes. Blood. 2009;114(5):937-951. doi:10.1182/blood-2009-03-209262

    • Search Google Scholar
    • Export Citation
  • 3.

    Jain NC. Classification of myeloproliferative disorders in cats using criteria proposed by the animal leukaemia study group: a retrospective study of 181 cases (1969-1992). Comp Haematol Int. 1993;3(3):125-134. doi:10.1007/BF00186096

    • Search Google Scholar
    • Export Citation
  • 4.

    Galemore ER, Labato MA, O’Neil E. Prevalence of Anaplasma phagocytophilum infection in feral cats in Massachusetts. JFMS Open Rep. 2018;4(1):2055116917753804. doi:10.1177/2055116917753804

    • Search Google Scholar
    • Export Citation
  • 5.

    Lobetti R, Lappin MR. Prevalence of Toxoplasma gondii, Bartonella species and haemoplasma infection in cats in South Africa. J Feline Med Surg. 2012;14(12):857-862. doi:10.1177/1098612X12452495

    • Search Google Scholar
    • Export Citation

Advertisement